This application addresses broad Challenge Area (06) Enabling Technologies and specific Challenge Topic, 06-MH-102: Technologies to study neuronal signaling, plasticity, and neurodevelopment. The complex and diverse functions of the brain depend on the unique properties of neural circuits formed by various subtypes of neurons with distinct molecular and/or electrical properties. Furthermore, many neurological disorders are often due to the dysfunction of specific subsets of neurons or neural circuits. Thus, elucidating the unique roles of each subtype of neurons in shaping circuitry function is critical for our understanding of both normal and abnormal brain functions. Genetic tools incorporating spatial and temporal control over neural activity in neuronal subsets would greatly enhance our capability to precisely map circuitry function and dysfunction in the brain. Manipulating activity in this way requires a tool that can be genetically targeted to specific populations of neurons and that allows simple and rapid control of neuronal firing. This has been made possible by the recent development of the genetically encoded light-activated cation channel channelrhodopsin-2 (ChR2) for photoactivation and the light-driven chloride pump halorhodopsin (NpHR) for photoinhibition. Recent studies from several laboratories have highlighted the tremendous potentials of using ChR2 and NpHR in mapping neuronal connectivity and manipulating circuitry function. The goal of this research proposal is to fully realize the potentials of these optogenetic tools by generating a series of transgenic mice that express improved ChR2 and NpHR selectively in molecularly defined subtypes of neurons in the brain, thus providing a set of powerful optogenetic mice for interrogating brain circuitry function and dysfunction using high-speed photostimulation and photoinhibition in brain slices and in vivo. PUBLIC HEALTH RELEVANCE: Abnormal neuronal connectivity and neuronal activity in the brain contribute to many neurological and neuropsychiatric disorders such as epilepsy and autism. The goal of this research proposal is to develop new genetic tools that will allow neuroscientists to manipulate neuronal activity in mouse models of human diseases, thus helping to elucidate the pathogenic mechanisms of neurological and neuropsychiatric disorders.